Method of manufacturing silicide layer for semiconductor device

ABSTRACT

It is made possible to reduce the interface resistance at the interface between the nickel silicide film and the silicon. A semiconductor manufacturing method includes: forming an impurity region on a silicon substrate, with impurities being introduced into the impurity region; depositing a Ni layer so as to cover the impurity region; changing the surface of the impurity region into a NiSi 2  layer through annealing; forming a Ni layer on the NiSi 2  layer; and silicidating the NiSi 2  layer through annealing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-363813 filed on Dec. 16, 2005in Japan, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the semiconductor device.

2. Related Art

The technology of producing silicon superintegrated circuits is one ofthe basic technologies that support the advanced information society inthe future. To achieve high-performance integrated circuits,high-performance CMOS devices that are the components of thoseintegrated circuits are essential. Although the scaling rule has beengenerally applied to high-performance devices, it is becoming difficultto produce higher-performance devices through ultra-miniaturization inrecent years, due to various physical limits. One example, there is aproblem of interface resistance in source and drain electrode regions.

A typical MOS transistor includes a gate insulating film that is formedon a silicon substrate, a gate electrode that is made of polysiliconformed on the gate insulating film, high-concentration impurity regionsthat are formed in portions of the silicon substrate located on bothsides of the gate electrode and are to be source and drain regions, andextension regions that connect to the high-concentration impurityregions and are formed with an impurity region provided in a portion ofthe silicon substrate located below the gate electrode. Further, asilicide film is provided on the gate electrode and thehigh-concentration impurity regions.

The silicide film provided on the high-concentration impurity regionsforms a Schottky junction between each high-concentration impurityregion and each corresponding extension region. The resistance on thedrain side is divided into the resistance of the silicide film (R_(sh)),the resistance of the drain region (R_(d)) caused by the bulk film, andthe interface resistance of the Schottky junction (R_(c)). Among thethree resistances, the interface resistance is generally known to be thehighest. Since the interface resistance does not decrease according tothe scaling rule, to reduce the interface resistance poses a veryimportant problem in improving the performances of MOS transistors inthe future.

Of the Schottky junctions formed between the silicide film and thehigh-concentration impurity regions, as to the Schottky junction on thedrain side, electrons that have reached the high-concentration impurityregion tunnel through the Schottky barrier height, towards the silicidefilm. The easiness of electron tunneling is generally referred to as thetunnel probability. The higher the tunnel probability is through ajunction, the lower the interface resistance is. The tunnel probabilityis known to exponentially decrease in relation to the product of theSchottky barrier height and the tunnel distance. Therefore, the Schottkybarrier height and the tunnel distance should be effectively reduced, soas to reduce the interface resistance.

One of the methods to do so involves segregating high-concentrationactivated impurities on the silicon side at the interface between thesilicide film and the silicon film (see R. L. Thornton, Elec. Lett., 17,485 (1981), and A. Kinoshita, SSDM, A-5-1 (2004), for example). Here, itis preferable to segregate the high-concentration activated impuritiesin a narrower range from the interface. Such an interface has the effectof improving the mirror effect and enhancing the bending of the siliconconduction band, so as to dramatically reduce the Schottky barrierheight and the tunnel distance. However, such an interface has not yetbeen produced to this day.

The processing technique for forming a metal silicide on the gateelectrode and the source and drain regions in a self-aligning fashion iscalled the SALICIDE (Self-aligned Silicide) process technique, which isan important technique for reducing the resistance in the gate electrodeand the source and drain regions in a CMOS device.

Conventionally, disilicides such as TiSi₂ and CoSi₂ having lowresistance among low-thermal metal silicides have been used for CMOSdevices. However, in the trend of ultra-miniaturization of devices, theuse of nickel monosilicide (NiSi) that has low sheet resistance andconsumes less silicon (Si) in the silicidation process is expected fornext-generation CMOS devices.

In the SALICIDE process, NiSi is considered to be beneficial, as itrequires a lower processing temperature than the currently used CoSi₂.Generally, nickel silicide has many phases. The phase of nickel silicidethat is formed at a lowest annealing temperature is dinickel silicide(Ni₂Si). As the annealing temperature rises, it changes to nickelmonosilicide (NiSi), and to nickel disilicide (NiSi₂). According to theconventional nickel SALICIDE process, nickel monosilicide (NiSi) isformed at last, as it has the lowest resistance. More specifically,after a Ni film is formed on a silicon film, annealing is performed at350° C. for 30 seconds, to form dinickel silicide (Ni₂Si). Annealing isthen performed at 500° C. for 30 seconds, to change the dinickelsilicide (Ni₂Si) into nickel monosilicide (NiSi).

To reduce the interface resistance at the interface between the nickelsilicide film and the silicon film poses one of the most crucialproblems with the nickel SALICIDE process that is expected to be putinto practical use for next-generation CMOS devices by the scaling rule.

In a sample that is formed with two silicon films into which typicalimpurities, arsenic (As) and boron (B), are introduced, a silicide filmis formed by the conventional nickel SALICIDE process, and the interfacebetween the nickel monosilicide (NiSi) and the silicon (Si) film isobserved through back-side SIMS (Secondary Ion Mass Spectroscopy). Theresults of the observation show that arsenic (As) is distributed on bothsides of the interface, but most of boron (B) is distributed in the NiSifilm. Therefore, a decrease in Schottky barrier height cannot beexpected in the high-concentration impurity region (a p-type siliconlayer) doped with boron (B). The results of actual experiments ofcurrent-voltage characteristics also show that an effective decrease inSchottky barrier height can hardly be seen.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and an object thereof is to provide a semiconductor device that canreduce the interface resistance at the interface between the nickelsilicide film and the silicon, and a method of manufacturing thesemiconductor device.

A method of manufacturing a semiconductor device according to a firstaspect of the present invention includes: forming an impurity region ona silicon substrate, with impurities being introduced into the impurityregion; depositing a Ni layer so as to cover the impurity region;changing the surface of the impurity region into a NiSi₂ layer throughannealing; forming a Ni layer on the NiSi₂ layer; and silicidating theNiSi₂ layer through annealing.

A semiconductor device according to a second aspect of the presentinvention includes: a MIS transistor which includes: a gate insulatingfilm that is provided on a semiconductor region of a first conductivitytype formed on a semiconductor substrate; a gate electrode that isprovided on the gate insulating film; gate sidewalls that are providedon side portions of the gate electrode and are made of an insulatingmaterial; and a silicide laminated film that is provided on the oppositeside of the semiconductor region from the gate electrode when seen fromthe gate sidewalls, the silicide laminated film including a NiSi₂ layerand a NiSi layer.

A semiconductor device according to a third aspect of the presentinvention includes: a p-type MIS transistor that comprises: a first gateinsulating film that is provided on an n-type first semiconductor regionformed on a semiconductor substrate; a first gate electrode that isprovided on the first gate insulating film; first gate sidewalls thatare provided on side portions of the first gate electrode and are madeof an insulating material; a p-type impurity region that is provided onthe opposite side of the first semiconductor region from the first gateelectrode to the first gate sidewalls; and a first silicide laminatedfilm that is provided on the p-type impurity region and includes a firstNiSi₂ layer and a first NiSi layer; and

an n-type MIS transistor that comprises: a second gate insulating filmthat is provided on a p-type second semiconductor region formed on thesemiconductor substrate;

a second gate electrode that is provided on the second gate insulatingfilm; second gate sidewalls that are provided on side portions of thesecond gate electrode and are made of an insulating material; an n-typeimpurity region that is provided on the opposite side of the secondsemiconductor region from the second gate electrode to the second gatesidewalls; and a second silicide laminated film that is provided on then-type impurity region and includes a second NiSi₂ layer and a secondNiSi layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method of manufacturing a semiconductordevice according to a first embodiment of the present invention;

FIGS. 2( a) to 2(e) are cross-sectional views illustrating the steps inthe manufacturing method according to the first embodiment;

FIG. 3 is a flowchart showing a method of manufacturing a semiconductordevice according to a second embodiment of the present invention;

FIGS. 4( a) to 4(f) are cross-sectional views illustrating the steps inthe manufacturing method according to the second embodiment;

FIG. 5 is a cross-sectional view illustrating a step for manufacturing asemiconductor device of Example 1;

FIG. 6 is a cross-sectional view illustrating a step for manufacturing asemiconductor device of Example 1;

FIG. 7 is a cross-sectional view illustrating a step for manufacturing asemiconductor device of Example 1;

FIG. 8 is a cross-sectional view illustrating a step for manufacturing asemiconductor device of Example 1;

FIG. 9 is a cross-sectional view illustrating a step for manufacturing asemiconductor device of Example 1;

FIG. 10 is a cross-sectional view illustrating a step for manufacturinga semiconductor device of Example 1;

FIG. 11 is a diagram for explaining the method of evaluating theSchottky barrier height at the interface between the nickel silicidelaminated film and the silicon film of each of the Schottky diodes ofExample 1 and Example 2;

FIG. 12 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 13 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 14 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 15 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 16 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 17 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 5;

FIG. 18 is a diagram showing the dependence of the drain current on thegate voltage in each of the MIS transistors of Example 5 and ComparativeExample 3;

FIG. 19 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 6;

FIG. 20 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 6;

FIG. 21 is a cross-sectional view illustrating a step for manufacturinga MIS transistor of Example 6;

FIG. 22 is a cross-sectional view showing a CMOS device of Example 9;

FIGS. 23A and 23B are a plan view and a front view showing a Fin channeltransistor of Example 10;

FIG. 24 is a cross-sectional view showing a Schottky transistor ofExample 11;

FIG. 25 is a flowchart showing a conventional nickel silicide process;

FIGS. 26A and 26B are diagrams showing the results of measurementcarried out through back-side SIMS on the arsenic and boron distributionin the vicinity of the interface between the NiSi film and the siliconfilm formed by the conventional nickel silicide process;

FIGS. 27( a), 27(b) and 27(c) are diagrams schematically showing theimpurity distribution in the vicinity of the interface between the NiSifilm and the silicon formed by the conventional nickel silicide process;

FIG. 28 is a diagram explaining the results of measurement carried outthrough back-side SIMS on the boron distribution in the vicinity of theinterface between the NiSi film and the silicon film formed by theconventional nickel silicide process;

FIG. 29 is a diagram showing the characteristics of a surface phase ofnickel silicide;

FIG. 30 is a diagram showing the formation energy in a case where B andAs are introduced into each phase of nickel silicide and silicon film;and

FIG. 31 is a diagram showing the difference in bending of the conductionband between silicon films due to the difference in dopant amountbetween the silicon films (silicon substrates).

DETAILED DESCRIPTION OF THE INVENTION

First, the background to the present invention is described, before theembodiments of the present invention are described.

FIGS. 26A and 26B shows the results of observations made throughback-side SIMS about the interface between NiSi and silicon films formedby a conventional nickel silicide process shown in FIG. 25. As shown inFIG. 25, in the conventional nickel silicide process, impurities arefirst introduced into a silicon film to form an impurity region (stepS51). A Ni film is then deposited on the impurity region by a sputteringtechnique or the like (step S52). RTA (Rapid Thermal Annealing) isperformed at 350° C. for 30 seconds, to form Ni₂Si (step S53). RTA isthen performed at 500° C. for 30 seconds, to form NiSi (step S54).

FIGS. 26A and 26B show the results of observations in cases wherearsenic (As) and boron (B) are introduced as impurities into theimpurity region of the silicon film. The region in which the nickeldistribution decreases is equivalent to the interface between thesilicon film and the NiSi film. When the interface does not rapidlychange, the interface has surface roughness, and the impuritydistribution averaged in the transverse direction is caught by theback-side SIMS. Accordingly, the mid point of the region in which thenickel concentration decreases can be regarded as the interface.

In the case where the conventional nickel silicide process is employed,As is distributed on both sides of the interface, as shown in FIG. 26A.Meanwhile, almost all of B is distributed in the NiSi film, as shown inFIG. 26B. As shown in FIG. 27( a), the impurities exist also in thesilicon film immediately after the Ni film is deposited on the siliconfilm (prior to the silicide formation). However, after the silicideformation, the impurities exist on both sides of the interface in thecase where the impurities are As, as shown in FIG. 27( b). In the casewhere the impurities are B type, most of the impurities exist in theNiSi film, as shown in FIG. 27( c). FIG. 28 shows the results ofmeasurement actually carried out through back-side SIMS on the Bdistribution in the vicinity of the interface between the NiSi and Sifilms. As described above, the region in which the nickel concentrationdecreases is equivalent to the interface. With the mid point of theregion in which the nickel concentration changes being the interface,the range of 20 nm on both sides are defined as a region D1 and a regionD2, respectively. As the B concentration is integrated in between, the Bconcentration is 4.2×10¹³ cm⁻² in the region D1, and is 7.92×10¹² cm⁻²in the region D2. As can be seen from the results, the amount of Bcontained in the NiSi film is the larger.

The inventors examined the reason that the impurity distributions at theinterface between the NiSi film and the Si film formed by theconventional process become as shown in FIGS. 26A and 26B, by usingfirst-principles calculation method.

The first-principles calculation method, including SP-GGA(Spin-Polarized Generalized Gradient Approximation) was used in thiscalculation. FIG. 29 shows the crystal structural data for nickelsilicides that were actually used in the calculations. The formationenergy with an impurity in a unit cell containing 12 atoms, 8 atoms, and12 atoms for the nickel silicide phases Ni₂Si, NiSi, and NiSi₂,respectively, was calculated. As for silicon (Si), the same calculationwas performed for a unit cell containing 64 atoms, and comparison witheach nickel silicide phase was performed. The formation energy in thecase where an impurity atom is introduced into nickel silicide andsilicon unit cells is defined as follows:

1) Formation energies in a case where impurities are introduced into thesilicon unit cell

The formation energy with an impurity atom in the interstice can beexpressed as:E _(f) ^(Int) =−E (a cell structure of 64 Si atoms containing oneimpurity atom)+E (a cell structure of 64 Si atoms)+E (one impurity atom in vacuum)

In a case where one impurity atom is substituted with one Si atom, theformation energy can be expressed as:E _(f) ^(Si) =−E (a cell structure of 63 Si atoms containing oneimpurity atom)−E (one bulk silicon atom)+E (a cell structure of 64 Si atoms)+E (one impurity atom in vacuum)

However, in the substitutional case, the substituted silicon atoms areassumed to move into the bulk silicon layer. For convenience, theformation energy in the case where one impurity atom is substituted withone silicon atom is represented by E_(f) ^(Si), and the formation energyin the case where one impurity atom is substituted with one nickel atomis represented by E_(f) ^(Ni).

2) Formation energy in a case where impurities are introduced into Ni₂Si

In a case where impurity atoms are introduced between the Ni₂Silattices, the formation energy can be expressed as:E _(f) ^(Int) =−E (a cell structure of 4 Ni₂Si atoms containing oneimpurity atom)+E (a cell structure of 4 Ni₂Si atoms)+E (one impurity atom in vacuum)

In a case where one impurity atom is substituted with one Si atom, theformation energy can be expressed as:E _(f) ^(Si) =−E (a cell structure having one Si atom among the fourNi₂Si atoms substituted with one impurity atom)−E (one Si atom in the bulk)+E (a cell structure of 4 Ni₂Si atoms)+E(one impurity atom in vacuum)

In a case where one impurity atom is substituted with one Ni atom, theformation energy can be expressed as:E _(f) ^(Ni) =−E (a cell structure having one Ni atom among the fourNi₂Si atoms substituted with one impurity atom)+( 7/2) E (one Ni₂Si atom)+E (one impurity atom in vacuum)+(½) E (onebulk Si atom)

However, in the case where an impurity atom is substituted with a Niatom, the substituted Ni atoms were considered to combine with one bulksilicon atom into Ni₂Si. Based on the above observations, the formationenergy was calculated according to the above equations.

3) Formation energy in a case where impurities are introduced into NiSiunit cell

As in the case where impurity atoms are introduced into Ni₂Si unit cell,in a case where impurity atoms are introduced between the NiSi lattices,the formation energy can be expressed as:E _(f) ^(Int) =−E (a cell structure of 4 NiSi atoms containing oneimpurity atom)+E (a cell structure of 4 NiSi atoms)+E (one impurity atom in vacuum)

In a case where one impurity atom is substituted with one Si atom, theformation energy can be expressed as:E _(f) ^(Si) =−E (a cell structure having one Si atom among the fourNiSi atoms substituted with one impurity atom)−E (one bulk silicon atom)+E (a cell structure of 4 NiSi atoms)+E (oneimpurity atom in vacuum)

In a case where one impurity atom is substituted with one Ni atom, theformation energy can be expressed as:E _(f) ^(Ni) =−E (a cell structure having one Ni atom among the fourNiSi atoms substituted with one impurity atom)+(one NiSi atom)+3E (one impurity atom in vacuum)+E (one bulk silicon atom)4) Formation energy in a case where impurities are introduced into NiSi₂

As in the case where impurity atoms are introduced into Ni₂Si or NiSiunit cells, in a case where impurity atoms are introduced between theNiSi₂ unit cells, the formation energy can be expressed as:E _(f) ^(Int) =−E (a cell structure of 4 NiSi₂ atoms containing oneimpurity atom)+E (a cell structure of 4 NiSi₂ atoms)+E (one impurity atom in vacuum)

In a case where one impurity atom is substituted with one Si atom, theformation energy can be expressed as:E _(f) ^(Si) =−E (a cell structure having one Si atom among the fourNiSi₂ atoms substituted with one impurity atom)−E (one bulk silicon atom)+E (a cell structure of 4 NiSi₂ atoms)+E (oneimpurity atom in vacuum)

In a case where one impurity atom is substituted with one Ni atom, theformation energy can be expressed as:E _(f) ^(Ni) =−E (a cell structure having one Ni atom among the fourNiSi₂ atoms substituted with one impurity atom)+3E (one NiSi₂ atom)+E (one impurity atom in vacuum)+2E (one bulksilicon atom)

FIG. 30 shows the results of calculations of formation energy. Ingeneral, the formation energy represents the difference between theinitial state of reaction and the final state of the reaction. A statehaving larger formation energy is considered to be easier to be realizedin an actual system. For example, as can be seen from the calculationresult in the case where boron (B) enters the silicon interstitial site,E_(f) ^(Si) is larger than E_(f) ^(Int), and accordingly, boron atomseasily enter the silicon substitution site. In the case of arsenic (As),E_(f) ^(Int) becomes a negative value, and As atoms cannot enter theinterstitial site but most As atoms enter the Si substitution site inthe final state.

Next, comparisons between the formation energy in a case whereimpurities enter the interstitial site of each phase of nickel silicideand the formation energy in a case where impurities enter the siliconinterstitial site are described. In the conventional nickel SALICIDEprocess shown in FIG. 25, Ni₂Si is generated in the first annealingprocedure. The formation energy in the case where B atoms enter theNi₂Si unit cells is larger than the formation energy in the case where Batoms enter the Si unit cells, whether the B atoms enter the Sisubstitution site or the interstitial site. Therefore, B atoms areconsidered to remain in the Ni₂Si layer during the silicidationprocedure.

Furthermore, even after NiSi is generated in the second annealingprocedure (step S54) shown in FIG. 25, the formation energy in theinterstice case is clearly larger than that in the case of silicon layerbut the difference of formation energy in the case of entering the Sisubstitutional site is very small between the NiSi and Si layers. Basedon this fact, B atoms can be considered to segregate toward the NiSifilm at the interface between the NiSi film and the Si film during thesilicidation procedure.

As for the case of As, the formation energy at the time of entering theSi substitution site in the case where the As atoms are introducedbetween Si unit cells is substantially equal to the formation energy ineither case of Ni₂Si unit cells or NiSi unit cells. Therefore, the Asatoms can be considered to segregate to both sides.

The same calculation as above was also performed for the NiSi₂ latticesgenerated through high-temperature annealing (750° C. or higher). Theresults show that the formation energy in either case where impurities(As or B) enter the interstitial site or the Si substitutional site issmaller than in the case of Si layers. Accordingly, once annealing isperformed at such a temperature as to generate NiSi₂, impurity atoms canbe segregated on the Si side at the interface, and the effect ofreducing the interface resistance can be expected.

However, the NiSi₂ film has high resistivity than the NiSi film, asshown in FIG. 29. Therefore, the generated NiSi₂ needs to be turned backinto NiSi.

In view of the above facts, the inventors considered that a Ni filmshould be formed on the NiSi₂ film by a sputtering technique, followedby annealing at 500° C. or lower to scatter the Ni atoms in the NiSi₂film. By doing so, the reaction of Ni+NiSi₂−>2NiSi occurs, and a NiSifilm is formed.

Embodiments of the present invention are as follows.

First Embodiment

Referring now to FIGS. 1 to 2( e), a method of manufacturing asemiconductor device according to a first embodiment of the presentinvention is described. FIG. 1 is a flowchart showing the procedures inthe manufacturing method according to this embodiment. FIGS. 2( a) to2(e) are schematic cross-sectional views showing the steps in themanufacturing method according to this embodiment.

First, as shown in step S1 of FIG. 1, impurities (such as boron (B)) areimplanted in a silicon substrate, to form an impurity region. A Ni filmis then deposited on the impurity region by a sputtering technique orthe like (step S2 of FIG. 1; see FIG. 2( a)). RTA is performed at 750°C. for 30 seconds, to form a NiSi₂ film (step S3 of FIG. 1; see FIG. 2(b)). The Ni that is not silicided is then removed with SH (a mixture ofsulfuric acid and hydrogen peroxide solution) (step S4 of FIG. 1). Next,Ni is again deposited on the NiSi₂ film by a sputtering technique, forexample (step S5 of FIG. 1; see FIG. 2( c)). RTA is then performed tosilicide the Ni (step S6 of FIG. 1).

If the annealing temperature in step S6 of FIG. 1 is high (higher than400° C. but not higher than 500° C., for example), the Ni atom diffusionin the NiSi₂ film is accelerated. Accordingly, NiSi is generated fromthe interface between the NiSi₂ film and the Si substrate, and a NiSifilm is formed between the NiSi₂ film and the Si substrate, as shown inFIG. 2E. If the annealing temperature is low (not higher than 400° C.for example), NiSi is generated on the opposite surface of the NiSi₂film from the Si substrate, and a NiSi film is formed on the NiSi₂ film,as shown in FIG. 2( d).

Whether the annealing temperature is high or low, the resultant silicidelayer is a laminated structure of a NiSi₂ film and a NiSi film. However,the thickness of the NiSi₂ film is very much smaller than the thicknessof the NiSi film, and the resistance of the silicide layer is lowaccordingly. The impurities introduced into the silicon substrate existalso on the sides of the silicon substrate, as shown in FIGS. 2( a) to2(e). This is reinforced by the evaluation result of the effectiveSchottky barrier height, as described later.

As described above, according to this embodiment, the interfaceresistance at the interface between the nickel silicide film and thesilicon (the silicon substrate) can be reduced.

In this embodiment and the later described second embodiment, if thethickness of a Ni film deposited on the NiSi₂ film by a sputteringtechnique is larger than the thickness of the NiSi₂ film, the Ni atomsremaining after all the NiSi₂ has changed to NiSi diffuse into the Sisubstrate, and the impurities once removed from the Si substrate arereturned into the Si substrate. Therefore, the thickness of the Ni filmformed on the NiSi₂ film by a sputtering technique should preferably besmaller than the thickness of the NiSi₂ film.

Second Embodiment

Referring now to FIG. 3 to 4( f), a method of manufacturing asemiconductor device according to a second embodiment of the presentinvention is described. FIG. 3 is a flowchart showing the procedures inthe manufacturing method according to this embodiment. FIGS. 4( a) to4(f) are schematic cross-sectional views showing the steps in themanufacturing method according to this embodiment.

First, as shown in step S11 of FIG. 3, impurities (such as boron (B))are implanted in a silicon substrate, to form an impurity region. A Nifilm is then deposited on the impurity region by a sputtering techniqueor the like (step S12 of FIG. 3; see FIG. 4( a)). RTA is performed at350° C. for 30 seconds, to form a Ni₂Si film (step S13 of FIG. 3). TheNi that is not silicided is then removed with a known chemical solution(step S14 of FIG. 3). NiSi is then formed through RTA at 500° C. for 30seconds (step S15 of FIG. 3; see FIG. 4( b)). The procedures up to thispoint are the same as the conventional nickel silicide process.

Next, NiSi₂ is formed through RTA at 750° C. for 30 seconds (step S16 ofFIG. 3; see FIG. 4( c)). Ni is then deposited on the NiSi₂ film by asputtering technique, for example (step S17 of FIG. 3; see FIG. 4( d)).RTA is then performed to silicide the Ni (step S18 of FIG. 3).

If the annealing temperature in step S18 of FIG. 3 is high (higher than400° C. but not higher than 500° C., for example), the Ni atom diffusionin the NiSi₂ film is accelerated as mentioned in the description of thefirst embodiment. Accordingly, NiSi is generated from the interfacebetween the NiSi₂ film and the Si substrate, and a NiSi film is formedbetween the NiSi₂ film and the Si substrate, as shown in FIG. 4( f). Ifthe annealing temperature is low (not higher than 400° C. for example),NiSi is generated on the opposite surface of the NiSi₂ film from the Sisubstrate, and a NiSi film is formed on the NiSi₂ film, as shown in FIG.4( e).

Whether the annealing temperature is high or low, the resultant silicidelayer is a laminated structure of a NiSi₂ film and a NiSi film. However,the thickness of the NiSi₂ film is very much smaller than the thicknessof the NiSi film, and the resistance of the silicide layer is lowaccordingly. The impurities introduced into the silicon substrate existalso on the sides of the silicon substrate, as shown in FIGS. 4( a) to4(f).

As described above, according to this embodiment, the interfaceresistance at the interface between the nickel silicide film and thesilicon (the silicon substrate) can be reduced, as in the firstembodiment.

In the following, the embodiments of the present invention are describedin greater detail by way of examples.

EXAMPLE 1

A semiconductor device of Example 1 of the present invention is nowdescribed. The semiconductor device of this example is a Schottky diodethat is manufactured by the manufacturing method of the secondembodiment shown in FIG. 3, and the annealing temperature at which eachsilicide film of a double-layer structure is formed is 400° C. Referringto FIGS. 5 to 10, a method of manufacturing the Schottky diode of thisexample is described.

First, as shown in FIG. 5, trenches that isolate device regions 6 and 8from each other are formed at 50 μm intervals on an n-type siliconsubstrate 2 doped with arsenic (As) with a concentration of 10¹⁵ cm⁻³.These trenches are filled with insulating film, to form device isolatinginsulating films 4 each having a STI (Shallow Trench Isolation)structure. A high-concentration impurity region 10 doped with boron (B)with a concentration of 10²⁰ cm⁻³ is formed in the range of thesubstrate surface to 300 nm in depth in each device region 8. Annealing(spike annealing) is then performed to activate impurities at 1050° C.

As shown in FIG. 6, a Ni film 11 of 12 nm in thickness is formed on theentire substrate surface by a sputtering technique. Annealing is thenperformed at 350° C. for 30 seconds, to form a Ni₂Si film (not shown).After the Ni that is not silicided is selectively removed with achemical solution, annealing is performed at 500° C. for 30 seconds, toform NiSi films 12 on the device regions 6 and 8, as shown in FIG. 7.The film thickness of each of the NiSi films 12 formed on the deviceregions 6 and 8 is 15 nm. The semiconductor device having the structureshown in FIG. 7 is the same as a Schottky diode manufactured by theconventional nickel silicide method.

Further, annealing is performed at 750° C. for 30 seconds, to change theNiSi films 12 to NiSi₂ films 14, as shown in FIG. 8. At this point, thethickness of each of the NiSi₂ films 14 is substantially the same as thethickness of each of the NiSi films 12, which is 15 nm. A Ni film 16 ofapproximately 10 nm in thickness is then formed on the entire substratesurface by a sputtering technique, as shown in FIG. 9. After annealingis performed at 400° C. for 30 seconds, the Ni that is not silicided isselectively removed with a chemical solution, so as to form nickelsilicide laminated films 19 on the device regions 6 and 8, as shown inFIG. 10. Each of the nickel silicide laminated films 19 has the NiSi₂film 14 as the lower layer (on the side of the silicon substrate) and aNiSi film 18 as the upper layer. The Schottky diode shown in FIG. 10will be hereinafter referred to as the Schottky diode of Example 1.

EXAMPLE 2

A semiconductor device of Example 2 of the present invention is nowdescribed. The semiconductor device of this example is a Schottky diodethat is manufactured by the manufacturing method of the secondembodiment shown in FIG. 3. This example is the same as Example 1,except that the annealing temperature at which each silicide film of adouble-layer structure is formed is 500° C. More specifically, thesemiconductor device of this example is manufactured in the same manneras in Example 1 until the procedures shown in FIG. 9. Annealing is thenperformed at 500° C. for 30 seconds, and the Ni that is not silicided isselectively removed with a chemical solution, thereby completing theSchottky diode of Example 2. Unlike in Example 1, each of the silicidelaminated film in the Schottky diode of this example has a NiSi film asthe lower layer (on the side of the silicon substrate) and a NiSi₂ filmas the upper layer.

EXAMPLE 3

A Schottky diode of Example 3 of the present invention is now described.The Schottky diode of this example is manufactured in the same manner asin Example 1, until the procedure shown in FIG. 8. The thickness of theNi film 16 deposited by a sputtering technique after the procedure shownin FIG. 8 is 20 nm, which is different from the thickness of the Ni film16 in Example 1. Accordingly, the thickness (=20 nm) of the Ni film 16is larger than the thickness (=15 nm) of each NiSi₂ film 14, unlike thecase in Example 1. After the Ni film 16 is deposited, annealing isperformed at 400° C. for 30 seconds, as in Example 1. The Ni that is notsilicided is selectively removed with a chemical solution, therebycompleting the Schottky diode of Example 3.

In the Schottky diode of this example, the thickness (=20 nm) of the Nifilm 16 is larger than the thickness (=15 nm) of each NiSi₂ film 14.Accordingly, all the NiSi₂ films 14 turn into the NiSi films 18, andeach silicide film has a single-layer structure of a NiSi film.

COMPARATIVE EXAMPLE 1

The Schottky diode manufactured in the same manner as the Schottky diodeof Example 1 until the procedure shown in FIG. 7 (the Schottky diodeshown in FIG. 7) is set as Comparative Example 1 with respect to Example1 to Example 3. In other words, the Schottky diode of ComparativeExample 1 is manufactured by the conventional nickel silicide process.

COMPARISONS AMONG THE EFFECTIVE SCHOTTKY BARRIER HEIGHTS OF THE SCHOTTKYDIODES OF EXAMPLE 1, EXAMPLE 2, AND COMPARATIVE EXAMPLE 1

In the following, comparisons among the effective Schottky barrierheights of the Schottky diodes of Example 1, Example 2, and ComparativeExample 1 are described.

As shown in FIG. 11, a terminal 100 was brought into contact with eachSchottky diode, so as to measure the current-voltage characteristics ofthis diode. Based on the voltage with which a current rises, theeffective Schottky barrier height at the interface between each nickelsilicide laminated film and the silicon substrate was evaluated. Themeasurement results showed that the effective Schottky barrier heightfor a hole was 0.3 eV in the Schottky diode of Comparative Example 1,0.1 eV in the Schottky diode of Example 1, and 0.14 eV in the Schottkydiode of Example 2. As can be seen from these results, the effectiveSchottky barrier height at the interface between each nickel silicidelaminated layer and the silicon substrate in each of the Schottky diodesof Example 1 and Example 2 manufactured by the nickel silicide processaccording to the second embodiment shown in FIGS. 3 to 4( f) is smallerthan the effective Schottky barrier height in the Schottky diodemanufactured by the conventional nickel silicide process shown in FIG.25 (Comparative Example 1). This proves that the semiconductor devicemanufacturing method according to the second embodiment has the effectof reducing the interface resistance at the interface between the nickelsilicide film and the silicon substrate.

COMPARISON BETWEEN THE INTERFACE STRUCTURES OF EXAMPLE 1 AND EXAMPLE 2

Next, the interface between each nickel silicide laminated film and thesilicon substrate of each of the Schottky diodes of Example 1 andExample 2 was observed through XRD (X-Ray Diffraction) and TEM-EDX(Transmission Electron Microscopy—Energy Dispersive X-Ray Spectrometer).The results showed that the interface between each nickel silicidelaminated film and the silicon substrate in Example 1 had the structureof NiSi film (18 nm)/NiSi₂ film (4 nm)/Si, while the interface inExample 2 had the structure of NiSi₂ film (4 nm)/NiSi film (18 nm)/Si.With the NiSi₂ film being formed on the surface, the impurities in thenickel silicide laminated films can segregate on the Si side at theinterface. Accordingly, the bending of the conduction band of the Sisubstrate becomes larger to reduce the effective Schottky barrierheight.

However, in either Example 1 or Example 2, the effective Schottkybarrier height is smaller than that at the Schottky interface formed bythe conventional nickel SALICIDE process, and it is confirmed that anexcellent interface with lower resistance can be produced.

Further, the region in the vicinity of the interface between each nickelsilicide laminated film and the silicon substrate in the Schottky diodeof Example 1, which is the range of 20 nm from the interface, wasobserved through back-side SIMS. The results showed that, unlike thecase of a conventional art shown in FIG. 28, a large amount of B atomsexisted on the side of the silicon substrate. Accordingly, the mirroreffect and the bending of the conduction band on the side of the siliconsubstrate become larger than in the conventional case, as shown in FIG.31, and the effective Schottky barrier height is reduced.

MEASUREMENT OF THE CURRENT-VOLTAGE CHARACTERISTICS OF THE SCHOTTKY DIODEOF EXAMPLE 3

In the Schottky diode of Example 3, all of the NiSi₂ film at theinterface turns into a NiSi film. Therefore, the B atoms released fromthe NiSi₂ film are partially returned to the reformed NiSi film, toreduce the bending of the conduction band in the Si layer. Accordingly,the measurement results show that the effective Schottky barrier heightin Example 3 is larger than the effective Schottky barrier height ineither of the Schottky diodes of Example 1 and Example 2. Because ofthis fact, the Ni film to be formed by a sputtering technique shouldpreferably be made thinner than the NiSi₂ film.

EXAMPLE 4

A Schottky diode of Example 4 of the present invention was produced. TheSchottky diode of Example 4 was formed on a p-type silicon substratedoped with boron (B) with a concentration of 10¹⁵ cm⁻³ throughsubstantially the same procedures as the procedures in the method ofmanufacturing the Schottky diode of Example 1 shown in FIGS. 5 to 10,except that the high-concentration impurity region 10 is doped with Aswith a concentration of 10²⁰ cm⁻³.

COMPARATIVE EXAMPLE 2

For comparison with the Schottky diode of Example 4, a Schottky diode ofComparative Example 2 having the structure shown in FIG. 7 was producedby the conventional nickel silicide process shown in FIG. 25. Like theSchottky diode of Example 4, the Schottky diode of Comparative Example 2has the high-concentration impurity region 10 doped with As with aconcentration of 10²⁰ cm⁻³.

COMPARISON BETWEEN THE EFFECTIVE SCHOTTKY BARRIER HEIGHT OF COMPARATIVEEXAMPLE 2 AND EXAMPLE 4

As shown in FIG. 11, a terminal 100 was brought into contact with eachSchottky diode, so as to measure the current and voltage between thenickel silicide laminated films. Based on the voltage with which acurrent rises, the effective Schottky barrier height at the interfacebetween each nickel silicide laminated film and the silicon substratewas evaluated. The evaluation results showed that the effective Schottkybarrier height with respect to electrons in the Schottky diode ofExample 4 is much smaller than that in the Schottky diode of ComparativeExample 2.

EXAMPLE 5

Next, a method of manufacturing an n-type MIS transistor in Example 5 ofthe present invention is described.

First, as shown in FIG. 12, trenches that isolate device regions 6 fromeach other are formed at 230 nm intervals on a p-type silicon substrate2 doped with boron (B) with a concentration of 10¹⁵ cm⁻³. These trenchesare filled with insulating film, to form device isolating insulatingfilms 4 each having a STI structure.

By a known technique, a device structure shown in FIG. 13 is then formedin the device regions 6 isolated from one another by the deviceisolating insulating films 4. This device structure is formed in thefollowing manner. A gate insulating film 22 having an equivalent oxidethickness (EOT) of 1 nm and a gate width of 30 nm is formed on eachdevice region 6, and a gate electrode 24 is then formed on the gateinsulating film 22. Extension regions 26 a and 26 b doped with As with aconcentration of 10²⁰ cm⁻³ are formed on both sides of the gateelectrode 24 in each device region 6. Gate sidewalls 28 made of aninsulating material are formed on the side portions of the gateelectrode 24. With the gate sidewalls 26 and the gate electrode 24serving as a mask, doping with As with a concentration of 10²⁰ cm⁻³ isperformed to form a source-side high-concentration impurity region 30 aand a drain-side high-concentration impurity region 30 b. After thedevice structure shown in FIG. 13 is formed, annealing for impurityactivation (spike annealing) is performed at 1050° C.

As shown in FIG. 14, a Ni film 32 of 12 nm in film thickness is thenformed by a sputtering technique. Annealing is performed at 750° C. for30 seconds, and a NiSi₂ film 34 is formed on the gate electrode 24 andthe source and drain regions 30 a and 30 b, as shown in FIG. 15. The Nithat is not silicided is selectively removed with a chemical solution.Thus, the device structure shown in FIG. 15 is produced. At this point,the thickness of each NiSi₂ film 34 is 15 nm.

A Ni film 36 of 10 nm in film thickness is formed by a sputteringtechnique, as shown in FIG. 16. Annealing is then performed at 400° C.for 30 seconds, and the Ni that is not silicided is selectively removedwith a chemical solution. As shown in FIG. 17, a nickel silicidelaminated film 38 that consists of the NiSi₂ film 34 and the NiSi film36 is formed on the gate electrode 24 and the source and drain regions30 a and 30 b. At this point, the nickel silicide laminated film 38 hasa NiSi film of 18 nm in thickness formed on a NiSi₂ film of 4 nm inthickness, as in the Schottky diode of Example 1. Thus, the n-type MIStransistor of Example 5 is completed.

COMPARATIVE EXAMPLE 3

For comparison with Example 5, an n-type MIS transistor is produced asComparative Example 3. More specifically, the device structure shown inFIG. 13 is formed through the same procedures as those of Example 5, anda silicide film on the gate electrode 24 and the source and drainregions 30 a and 30 b is formed by the conventional nickel silicideprocess shown in FIG. 25. This MIS transistor of Comparative Example 3is produced through exactly the same procedures as those of Example 5until the procedure shown in FIG. 13. After a Ni film is deposited onthe entire substrate surface, annealing is performed at 350° C. for 30seconds, to form a Ni₂Si film. The Ni that is not silicided is thenselectively removed with a chemical solution. Annealing is nextperformed at 500° C. for 30 seconds, to change the Ni₂Si film into aNiSi film. Thus, the n-type MIS transistor of Comparative Example 3 iscompleted. At this point, the film thickness of the NiSi film is 15 nm.

Next, we show the dependence of drain current on gate voltage in each ofthe MIS transistors of Example 5 and Comparative Example 3,

As can be seen from FIG. 18, the dependence of the drain current on thegate voltage in the MIS transistor of Example 5 shows a 30% currentincrease in comparison with the MIS transistor of Comparative Example 3,due to the decrease in interface resistance in the source and drainregions.

EXAMPLE 6

Next, a method of manufacturing a MIS transistor of Example 6 isdescribed. Although the extension regions 26 a and 26 b are formedbefore the formation of the high-concentration impurity regions 30 a and30 b in Example 5, the extension regions 26 a and 26 b may be formedafter the formation of the high-concentration impurity regions 30 a and30 b. The manufacturing method of this example is the same as themanufacturing method of Example 5, except that the extension regions 26a and 26 b are formed after the formation of the high-concentrationimpurity regions 30 a and 30 b.

First, as shown in FIG. 19, a gate insulating film 22 is formed on eachof device regions 6 isolated from one another by device isolatinginsulating films 4, and a gate electrode 24 is formed on the gateinsulating film 22. Gate sidewalls 25 that are made of an insulatingmaterial and are used for impurity injection are formed on the sideportions of the gate electrode 24. As the gate sidewalls 25 and the gateelectrode 24 serving as a mask, impurities, such as As, are injected toform high-concentration impurity regions 30 a and 30 b. Activationannealing (spike annealing) is then performed at 1050° C.

As shown in FIG. 20, the gate sidewalls 25 are removed. With the gateelectrode 24 serving as a mask, shallower injection of impurities Asthan in the case of the high-concentration impurity regions 30 a and 30b is carried out to form the extension regions 26 a and 26 b. Afteractivation annealing such as FLA (Flash Lamp Annealing) or laserannealing is performed, gate sidewalls 28 also made of an insulatingmaterial are formed on the side portions of the gate electrode 24,thereby completing the device structure shown in FIG. 13. By thisprocess, the influence of high-temperature activation annealing on theextension regions can be reduced.

The same procedures as those of Example 5 shown in FIGS. 14 to 17 arethen carried out to form an n-type MIS transistor of Example 6. As inthe MIS transistor of Example 5, the current in the MIS transistor ofExample 6 can be made approximately 30% higher than the current in theMIS transistor of Comparative Example 3.

EXAMPLE 7

Next, a semiconductor device of Example 7 of the present invention isdescribed. The semiconductor device of this example is a p-type MIStransistor that is the same as the MIS transistor of Example 5, exceptthat the silicon substrate 2, the extension regions 26 a and 26 b, andthe high-concentration impurity regions 30 a and 30 b each have theopposite conductivity from that in Example 5. As in the MIS transistorof Example 5, the current in the p-type MIS transistor of Example 7 canalso be made approximately 30% higher than the current in the MIStransistor of Comparative Example 3.

EXAMPLE 8

Next, a semiconductor device of Example 8 of the present invention isdescribed. The semiconductor device of this example is a p-type MIStransistor that is the same as the MIS transistor of Example 6, exceptthat the silicon substrate 2, the extension regions 26 a and 26 b, andthe high-concentration impurity regions 30 a and 30 b each have theopposite conductivity from that in Example 6.

In this example, the influence of high-temperature activation annealingon the extension regions can be reduced, as in Example 6. Also, as inthe MIS transistor of Example 6, the current in the p-type MIStransistor of Example 8 can be made approximately 30% higher than thecurrent in the MIS transistor of Comparative Example 3.

EXAMPLE 9

FIG. 22 illustrates a semiconductor device of Example 9 of the presentinvention. The semiconductor device of this example is a CMOS device.

In the CMOS device of this example, a p-well 42 and an n-well 44 thatare isolated from each other by a device isolating insulating film 46are formed on a p-type silicon substrate 40. An n-type transistor isprovided on the p-well 42, and a p-type MOS transistor is provided onthe n-well 44.

The n-type MOS transistor includes the MIS transistor of Example 5 andpocket regions 53, while the p-type MOS transistor includes the MIStransistor of Example 7 and pocket regions 55. Besides that, the n-typeMOS transistor and the p-type MOS transistor have the same structures.More specifically, in the n-type MOS transistor, a gate insulating film48 is provided on the p-well 42, and a gate electrode 50 a is providedon the gate insulating film 48. Gate sidewalls 56 are formed on the sideportions of the gate electrode 50 a, and n⁺-type high-concentrationimpurity regions 58 are formed in the p-well 42 on both sides of thegate electrode 50 a. Further, n⁻-type extension regions 52 that connectto the high-concentration impurity regions 58 are formed in the portionof p-well 42 immediately below the gate electrode 50 a. Below theextension regions 52, p⁺-type pocket regions 53 to which p-typeimpurities are injected are provided. A silicide film 66 of a laminatedstructure including a NiSi₂ film 62 and a NiSi film 64 is formed overthe high-concentration impurity regions 58 and the gate electrode 50 a.

Meanwhile, in the p-type MOS transistor, a gate insulating film 48 isprovided on the n-well 44, and a gate electrode 50 b is provided on thegate insulating film 48. Gate sidewalls 56 are formed on the sideportions of the gate electrode 50 b, and p⁺-type high-concentrationimpurity regions 60 are formed in the n-well 44 on both sides of thegate electrode 50 b. Further, p⁻-type extension regions 54 that connectto the high-concentration impurity regions 60 are formed in the portionof n-well 44 immediately below the gate electrode 50 b. Below theextension regions 54, n⁺-type pocket regions 55 to which n-typeimpurities are injected are provided. A silicide film 66 of a laminatedstructure including a NiSi₂ film 62 and a NiSi film 64 is formed overthe high-concentration impurity regions 60 and the gate electrode 50 b.

The n-type MOS transistor and the p-type MOS transistor operate in acomplementary fashion, thereby forming the CMOS device. Like each of theMIS transistors of Example 5 to Example 8, the CMOS device of Example 9can be formed by forming a Ni film by a sputtering technique after theformation of a NiSi₂ film, and performing annealing at 500° C. or lower.Thus, the resistance in the source and drain regions can be reduced, andthe drive current can be increased, as in each of the MIS transistors ofExample 5 to Example 8.

EXAMPLE 10

FIGS. 23A and 23B illustrate a semiconductor device of Example 10 of thepresent invention. The semiconductor device of this example is a Finchannel transistor. FIG. 23A is a plan view of the Fin channeltransistor, and FIG. 23B is a front view of the Fin channel transistor.

In the Fin channel transistor of this example, semiconductor regions areprovided between a source region 74 and a drain region 76, and a gateelectrode 72 is formed across the semiconductor regions. Thesemiconductor regions located below the gate electrode 72 serve aschannel regions. With this structure, current flows through more thanone channel, and the current value can be increased accordingly.

As in each of the MIS transistors of Example 5 to Example 8, in the Finchannel transistor of this example, a nickel silicide laminated film 80having a laminated structure of a NiSi₂ film and a NiSi film is providedon the gate electrode 72, the source region 74, and the drain region 76.With this arrangement, the interface resistance at the interface betweenthe nickel silicide film and the silicon substrate can be reduced, as ineach of the MIS transistors of Example 5 to Example 8. Thus, theresistance in the source and drain regions can be reduced, and the drivecurrent can be increased. Further, sidewalls 78 that are made of aninsulating material are provided to surround the gate electrode 72, thesource region 74, and the drain region 76.

EXAMPLE 11

FIG. 24 illustrates a semiconductor device of Example 11 of the presentinvention. The semiconductor device of this example is an n-typeSchottky source-drain MIS transistor (hereinafter also referred tosimply as a Schottky transistor). In this n-type Schottky MIStransistor, device regions 92 that are isolated from one another bydevice isolating insulating films 91 are provided on a p-type siliconsubstrate 90. A gate insulating film 93 is provided on each of thedevice regions 92, and a gate electrode 94 is formed on the gateinsulating film 93. Gate sidewalls 95 that are made of an insulatingmaterial are provided on the side portions of the gate electrode 94, anda silicide laminated film 96 to be a source and a drain is formed in theportions of the device region 92 located outside the gate sidewalls 95.This silicide laminated film 96 has a laminated structure of a NiSi₂film and a NiSi film, and is also placed on the gate electrode 94. Thesilicide laminated film 96 is manufactured by the same process as thatexplained in the descriptions of Example 5 to Example 8.

The n-type Schottky MIS transistor of this example differs from any ofthe MIS transistors of Example 5 to Example 8 in that the gate sidewalls95 are thinner and the high-concentration impurity regions are notprovided. More specifically, the Schottky transistor of this example isa transistor that does not have high-concentration impurity regions buthas a silicide film formed directly on a silicon semiconductorsubstrate. In this transistor, the pn junction formed between thehigh-concentration impurity regions and the silicon substrate of each ofExample 5 to Example 8 is replaced with a Schottky junction.Accordingly, problems such as a short channel effect and parasiticresistance that are likely to be caused when the MIS transistor becomessmaller according to the scaling rule can be effectively avoided.

As in each of the MIS transistors of Example 5 to Example 8, in then-type Schottky source-drain MIS transistor, the interface resistance atthe interface between the nickel silicide film and the silicon can bereduced. Thus, the resistance in the source and drain regions can bereduced, and the drive current can be increased.

EXAMPLE 12

Next, a semiconductor device of Example 12 of the present invention isdescribed. The semiconductor device of this example is a p-type Schottkysource-drain MIS transistor (also referred to simply as a Schottkytransistor), and is manufactured in the same manner as the Schottkytransistor of Example 11, except that it is formed on an n-type siliconsubstrate. As in the MIS transistor of Example 11, in the p-typeSchottky source-drain MIS transistor, the interface resistance at theinterface between the nickel silicide film and the silicon can bereduced. Thus, the resistance in the source and drain regions can bereduced, and the drive current can be increased.

As described so far, in each of the examples, the interface resistanceat the interface between the nickel silicide film and the silicon can bereduced.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcepts as defined by the appended claims and their equivalents.

1. A method of manufacturing a semiconductor device, comprising: formingan impurity region on a silicon substrate, with impurities beingintroduced into the impurity region; depositing a Ni layer so as tocover the impurity region; changing the surface of the impurity regioninto a NiSi₂ layer through annealing; forming a Ni layer on the NiSi₂layer; and silicidating the NiSi₂ layer through annealing.
 2. The methodof manufacturing a semiconductor device as claimed in claim 1, wherein afilm thickness of the Ni layer deposited on the NiSi₂ layer is smallerthan a film thickness of the NiSi₂ layer.
 3. The method of manufacturinga semiconductor device as claimed in claim 1, wherein the silicidationof the NiSi₂ layer includes forming a silicide laminated film includinga NiSi₂ layer and a NiSi layer.
 4. The method of manufacturing asemiconductor device as claimed in claim 1, wherein the silicidation ofthe NiSi₂ layer includes performing annealing at a temperature of 500°C. Or lower.
 5. The method of manufacturing a semiconductor device asclaimed in claim 4, wherein the silicidation of the NiSi₂ layer includesperforming annealing at a temperature of 400° C. Or lower.
 6. The methodof manufacturing a semiconductor device as claimed in claim 1, whereinthe changing of the surface of the impurity region into a NiSi₂ layercomprising: changing the surface of the impurity region into a Ni₂Silayer through annealing; changing the Ni₂Si layer into a NiSi layerthrough annealing; and changing the NiSi layer into a NiSi₂ layerthrough annealing.